1. Technical Field
This disclosure relates to semiconductor fabrication, and more particularly, to methods for forming a single sided buried strap on one side of the trench while protecting a collar dielectric on the other side of the trench.
2. Description of the Related Art
To reduce memory cell size and increase the density of devices formed on a semiconductor chip, vertical transistors have been developed. Memory devices, such as dynamic random access memories (DRAM) may include vertical transistors. Vertical transistors are formed by providing a trench in a substrate and forming a dielectric collar on sidewalls of the trench. A storage node is formed in the trench and recessed to provide access to substrate walls. A buried strap is formed in the recess by depositing a highly doped material in the trench. For vertical transistors, a single side buried strap may be employed. This single-sided strap is formed by methods, which may cause damage to the collar on the opposite side of the trench. In these cases, the collar would not provide adequate protection from the adjacent device.
Therefore, a need exists for a fabrication method which removes a portion of a dielectric collar to form a single-sided buried strap without damage to portions of the collar, which are to remain in the trench.